Studies of weight loss in obese diabetic and non-diabetic adults will be supplemented by studies employing exercise training in similar individuals to help elucidate the inter-relationship of glucose tolerance, insulin sensitivity and gluco-regulatory hormone levels. The effects of exercise training or weight loss on glucose tolerance tests, glucose disposal during glucose clamp, insulin secretory responses to various stimuli, 24 hr. urinary C-peptide excretion, tissue lipoprotein lipase activities, and body composition will be examined. The magnitude of the exercise training effect will be followed by measurements of maximal oxygen uptake capacity. Measurement of heat production (or thermogenesis) during weight loss or gain will suggest whether differences in energy conservation predispose toward obesity in the Pima Indians. These studies will provide much needed information on the effectiveness and limitations of weight loss and/or exercise programs in the treatment of obesity and type II diabetes.